Process of vulcanizing chloroprene polymers



No Drawing. Filed July 17, 1959, Ser. No. 827,732 Claims. (Cl. 260-795)This invention is directed to an improvement in the process ofvulcanizing polychloroprene, commercially known as neoprene. Accordingto this invention, neoprene is vulcanized using accelerators which areactive at ordinary vulcanization temperatures but which provide a muchwider margin of processing safety than do the currently usedaccelerators.

Neoprene is a generic name which is applied to polymers of2-chloro-1,3-butadiene (chloroprene) and interpoiymers of chloroprenewith dienes or vinyl compounds such as acrylonitrile, 1,3-butadiene,isoprene, 2,3-dichloro- 1,3-butadiene, and styrene in whichinterpolymers chloroprene comprises the predominant monomer (50% or moreby Weight). These polymers and interpolymers are usually made in aqueousemulsions and are available on the market today as solid polymers undernames such as Neoprene type GN, Neoprene type GRT, Neoprene type W,Neoprene type AC, Neoprene type WHV, Neoprene type WX, and Neoprene typeWR as fluid polymers such as Neoprene type PB and as latices under typenumbers such as type 571, type 750, and type 842A, all of which aregenerally referred to as polychloroprenes or chloroprene polymers.

Polychloroprenes difier greatly from other synthetic rubbers and fromnatural rubber in the manner in which they can be vulcanized. With mosttypes of polychloroprene, good vulcanizates may be obtained by incorpo-States Patent rating certain metal oxides, such as zinc oxide andmagnesia, in the plastic polymer and heating to eflect vulcanization.However, it is customary to use, in conjunction with the metal oxides,certain organic accelerators which increase the rate of cure and improvethe properties of the vulcanizates. With some types of polychloroprene,such as those which are made in the presence of aliphatic mercaptans,metal oxides act slowly and do not produce a high state of cure evenafter long periods of heating. With polychloroprenes of this type,accelerators are necessary for a good cure.

Among the polychloroprene accelerators in current use areZ-mercapto-Z-imidazoline, and the di-o-tolylguam'dine salt of dicatecholborate. These accelerators produce excellent polychloroprenevulcanizates. However, because of their activity at relatively lowtemperatures, care must be taken to prevent premature vulcanization(scorching) during the processing. This problem of scorch is mostnoticeable in the case of polychloroprenes which are made in thepresence of aliphatic mercaptans.

It is an object of this invention to provide improved accelerators forneoprene which are active at ordinary vulcanization temperatures butwhich give a wide margin of processing safety. It is a further object ofthis invention to provide accelerators for chloroprene polymers whichenable one to obtain significantly good vulcanizates of polychloroprenefree of premature scorching during the processing of saidpolychloroprene. These and other objects will become apparent in thefollowing description and claims.

and heating to efiect curing of the polymer.

The chloroprene polymers which can be cured b the improved process ofthe subject invention include homopolymers of chloroprene andinterpolymers containing at least 50 weight percent chloroprene and atleast one other monomer. Representative examples of suitable monomersare described in US. Patents 2,029,410; 2,066,329; 2,066,330 and2,066,331.

The accelerators of this invention may be used in amounts ranging from0.3 to 5.0 parts by weight per parts of polymer. Amounts lower than 0.3part give unsatisfactory cures and there would be no advantage in usingmore than 5.0 parts. The preferred amounts are 0.5 to 1.5 parts.

Magnesia and zinc oxide are both present as curing agents. The magnesiaconcentration ranges from about 0.5 to 15 parts by weight per 100 partsof polymer; 4 parts are preferred. The Zinc oxide concentration rangesfrom about 2 to 15 parts by weight per 100 parts of polymer; 5 parts arepreferred.

Sulfur or any of the antioxidants (such as phenyl-beta naphthylamine,phenyl-alpha-naphthylamine, or 2,2-methylenebis(4-methyl-6-tertiary-butylphenol), coloring matters, andother types of compounding ingredients commonly used in fabricatingpolychloroprene articles may be incorporated prior to cure.

The vulcanization may be carried out from C. to 200 C. The preferredrange is C. to C. Vulcanization may be carried out in molds under pressure, or the shaped articles may be heated with steam or hot air ortreated in a hot liquid bath. These accelerators may also be used inlatex or cements.

The compounds of this invention may be prepared by the reaction ofethylenethiourea(2-mercapto-2-imidazoline) with 1,4-dichloro-2-butene orethylenedibromide.

Representative examples illustrating the present invention are asfollows. 1

Example A.Preparation of 2,2'-(Z-butenylenedithio) di- Z-imidazoline Asuspension of 500 g. (4.9 moles) of ethylenethiourea in 3.5 liters ofwater was heated at 65-75 C., with agitation, with 305 g. (2.44 moles)of 1,4-dichloro-2-butene until the solid and oil were taken up in theaqueous phase. The solution was cooled below room temperature andtreated with 200 g. (5 moles) of sodium hydroxide pellets in 2.35 litersof water. The product was collected on a filter, washed with water andethyl alcohol, in turn, and dried at 40 C. under reduced pressure.

The compound showed the following analysis. Calculated for O d-1 N 8 C,46.9; H, 6.25; N, 21.9; S, 25.0; Found: C, 47.1; H, 6.4; N, 21.7; S,24.8.

Example B. Preparation of .2,2'-ethylenedithi0di-2- imzdazalin'e2,2'-ethylenedithiodi-2-imidazoline was prepared from ethylenethiourea(2 moles) and ethylene dibromide (1 mole) in a manner similar to thatused for 2,2-(2-butenylenedithio) di-Z-imidazoline, as described inExample A.

Example 1 Polychloroprene was compounded according to the fol-Accelerator, as shown in Table I.

1:"olyehloroprene prepared by the emulsion polymerization of chloroprenein the presence of an aliphatic mercaptan as a modifier as described in11.8. Patent 2,494,087.

The compound stock was cured in a mold in a press at 153 C. for 15minutes. The cured product was tested according to A.S.T.M. standardD412- IT. The Mooney scorch data were obtained according to A.S.T.M.standard D-l077-55T.

Table I shows the test results and gives a comparison of2,2-(Z-butenylenedithio)di 2 imidazoline with 2 -'mercapto2-imidazoline.

The polychloroprene of Example 1 was compounded according to thefollowing formula to yield a black stock:

Parts Polychloroprene 100 Phenyl-betamaphthylamine .1 Magnesia 4 Stearicacid 0.5 Semi-reinforcing furnace carbon black 29 Zinc oxide 5Accelerator, as shown in Table H.

The compounded stock was cured in a mold in apress for 30 minutes at 153C. Table H shows the results of the tests.

TABLE II 2-mer- 2,2-(2-butenylenedithio)- captodi-Z-imidazoline, partsZ-imidazoline, i 0.5 part 0.64 0.80 0.90 0.96

Modulus at 300% elongation,

psi 1,875 1, 425 1, 600' 1,540 1, 825 Tensile strength at break,

pis. 3,150 3,400 3,100 3,370 3,550 Elongation at break, percent" 430 540490 500 480 Mooney scorch min. for

point rise above minimum 2 value (121 0.). 33 '28 28, 33 Minimum reading'27 v '28 V '27 28; 27

Example 3 The polychloroprene of Example 1 was compounded according tothe formula of Example 2. 2,2-ethylenedithiodi-Z-imidazoline was used inthe proportions shown in Table III. The compounded stock was cured in amold in a press at 153 C. for 30 minutes. Table III shows the results ofthe tests.

The heretofore described polymers of chloroprene (2-chloro-l,3-butadiene) and interpolymers of chloroprene with dienes orvinyl compounds in which interpolymers thechloroprene comprises thepredominant monomer may be substituted in any of the preceding specificrepresentative examples to give substantially the same results.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A process of vulcanizing chloroprene polymers wherein zinc oxide,magnesia and from 0.3 to 5.0 parts by weight per parts of the polymer ofthe compound having the formula having the formula H N S-CHr-CHz-S N r5% i i H2GN N- CH2 are incorporated into said chloroprene polymerfollowed by heating to effect curing of said chloroprene polymer.

5. The process of claim 4'carried out at a temperature within the rangeof C. to 200 C.

6. The process of claim 4 wherein the chloroprene polymer ispolychloroprene.

7. A process of vulcanizing chloroprene poly wherein zinc oxide,magnesia and from 0.3 to 5.

by weight per 100 parts of the polymer of the compound having theformula are incorporated into said chloroprene polymer followed byheating to effect curing of said chloroprene polymer.

6 8. The process of claim 7 carried out at a temperature within therange of 125 C. to 200 C.

9. The process of claim 7 wherein the chloroprene poly mer ispolychloroprene.

References Cited in the file of this patent UNITED STATES PATENTS2,544,746 Baum Mar. 13, 1951

1. A PROCESS OF VULCANIZING CHLOROPRENE POLYMERS WHEREIN ZINC OXIDE,MAGNESIA AND FROM 0.3 TO 5.0 PARTS BY WEIGHT PER 100 PARTS OF THEPOLYMER OF THE COMPOUND HAVING THE FORMULA